The folks at Instagram wrote up a great post talking on their Blog talking about how they use Open Source and the other technologies.  The article gives some great insight into how they do business and where they have decided to spend their infrastructure dollars.  The big technology they rely on is Ubuntu, Amazon EC2 and S3, PostgreSQL, and a bunch more open tools.  While they don’t give any secrets away they do a nice job of showing what they use on a day to day basis.  Check it out.